On 20 January 2011 10:58, Henning Thielemann
Wolfgang Jeltsch wrote:
If both (>>=) and join are class methods with default implementations that use the respective other method, you can still define the Cont monad instance in terms of (>>=), while you can use join where it is easier (e.g. in the [] instance). So instead of arguing whether join or (>>=) is easier, more natural or whatever, just let us make both a method of Monad.
Does anyone want to comment on my comparison with restricted monads, where '>>=' can be defined, but 'join' cannot?
Just for clarity, are you referring to the restricted monads from the rmonad package[1]? If so, I see no reason (yet) why the RMonad type class can't be defined as: class RMonad m where join :: Suitable m a => m (m a) -> m a Where the Set instance becomes: instance RMonad Set where join ss = withResConstraints $ \SetConstraints -> fold union empty ss Regards, Bas [1] http://hackage.haskell.org/package/rmonad